The present invention relates to magnetic recording technology, and more particularly to a giant magnetoresistive read head which is capable of being used at high magnetic recording densities and which has reduced noise.
Magnetoresistive (xe2x80x9cMRxe2x80x9d) heads are currently used in read heads or for reading in a composite head. FIGS. 1A and 1B depict a conventional MR head 10 which uses a MR sensor 30, preferably a spin valve. FIG. 1A depicts a side view of the conventional MR head 10. For clarity, only a portion of the conventional MR head 10 is depicted. Also shown is the surface of the recording media 40. Thus, the air-bearing surface (ABS) is shown. Depicted in FIG. 1A are the first shield 14, the second shield 22, the MR sensor 30 and the leads 19a and 19b. Also shown is the height of the MR sensor 30, also known as the stripe height (h).
FIG. 1B depicts the conventional MR head 10 as viewed from the ABS. The MR head 10 includes a first shield 14 formed on a substrate 12. The MR head 10 also includes a first gap 16 separating a MR sensor 30 from the first shield 14. The MR head 10 also includes a pair of hard bias layers 18a and 18b. The hard bias layers 18a and 18b magnetically bias layers in the MR element 30. The MR head 10 also includes lead layers 19a and 19b, which conduct current to and from the MR sensor 30. A second gap 20 separates the MR sensor 30 from a second shield 22. When brought in proximity to a recording media (not shown), the MR head 10 reads data based on a change in the resistance of the MR sensor 30 due to the field of the recording media. Thus, the current through the MR sensor flows across the ABS, for example from left to right, or vice-versa, in both FIGS. 1A and 1B.
Giant magnetoresistance (xe2x80x9cGMRxe2x80x9d) has been found to provide a higher signal for a given magnetic field. Thus, GMR is increasingly used as a mechanism for conventional higher density MR sensors 30. One MR sensor 30 which utilizes GMR to sense the magnetization stored in recording media is a conventional spin valve. FIG. 1C depicts one conventional GMR sensor 30, a conventional spin valve. The conventional GMR sensor 30 typically includes a seed layer 31, a pinning layer that is typically an antiferromagnetic (xe2x80x9cAFMxe2x80x9d) layer 32, a pinned layer 34, a spacer layer 36, a free layer 38, and a capping layer 39. The seed layer is used to ensure that the material used for the AFM layer 32 has the appropriate crystal structure and is antiferromagnetic in nature. The spacer layer 36 is a nonmagnetic metal, such as copper. The pinned layer 34 and the free layer 38 are magnetic layers, such as CoFe. The magnetization of the pinned layer 34 is pinned in place due to an exchange coupling between the AFM layer 32 and the pinned layer 34. The magnetization of the free layer 38 is free to rotate in response to the magnetic field of the recording media 40. However, note that other conventional GMR sensors, such as conventional dual spin valves, conventional synthetic spin valves, and spin filters, are also used.
More recently, another configuration for conventional MR heads has been disclosed. FIG. 2 depicts a side view of a conventional MR head 50 in which current is driven perpendicular to the ABS. Also depicted is the recording media 40. The MR head 50 utilizes the MR sensor 30. Thus, the MR head 50 typically uses some sort of spin valve as the MR sensor 30. However, the MR head 50 could use another type of MR sensor (not shown), such as an AMR sensor. Regardless of the type of MR sensor used, the MR head 50 uses a vertical sensor, through which current is driven perpendicular to the ABS. As viewed from the ABS, the MR sensor 30 would generally appear as shown in FIG. 1C.
Referring back to FIG. 2, the MR head 50 also includes the first shield 52, the first gap 54, a conductor 56 that connects the MR sensor 30 to the first shield 52, the lead 58, the second gap 60 and the second shield 62. Also shown is the stripe height of the MR sensor 30, h, and the read gap 64. Current is driven through the MR sensor 30 between the first shield 52 and the lead 58. Thus, current is either parallel or antiparallel to the current direction 66 depicted in FIG. 2.
The conventional MR head 50 has advantages over the conventional MR head 10. In particular, the conventional MR head 50 may be more suitable for reading higher areal density media because of the direction of current flow through the MR head 50. The desired resistance of the MR sensor 30 can be provided in the MR head 50 by adjusting the stripe height, h. At the same time, the width of the MR sensor 30, as seen from the air-bearing surface (left to right in FIG. 1B), can be made small enough to be used with recording media 40 having a smaller track width. Thus, the conventional MR head 50 is of interest for high areal density recording applications.
Although the conventional MR head 50 functions, one of ordinary skill in the art will readily realize that there are drawbacks to the conventional MR head 50. Referring to FIGS. 1A-C and 2, the MR sensor 30 of the conventional MR head 50 is subject to noise due to domain wall motion. In contrast to the MR head 10, the MR sensor 30 does not magnetically bias the free layer 38 of the MR sensor 30. The materials used to magnetically bias the free layer 38 in the MR head 10 are typically conductive hard magnetic layers 18a and 18b that are placed adjacent to the free layer 38 as viewed from the ABS. These hard magnetic layers are typically materials such as CoCrPt and CoPt, which are conductive. However, if such hard magnetic layers 18a and 18b are placed at the sides of the free layer 38 in the conventional MR head 50, the hard magnetic layers 18a and 18b will shunt current away from the MR sensor 30. The signal from the MR sensor 30 would thus be lowered, which is undesirable.
In order to prevent the shunting of current away from the MR sensor 30 in the conventional MR head 50, no hard magnetic layers are used. However, this results in a free layer 38 of the MR sensor 30 that may have multiple domains. When the free layer 38 is subject to an external field, for example from the recording media 40, the magnetization of the free layer 38 changes in response to the external field. The walls between the domains in the free layer 38 move to change the magnetization of the free layer 38. The domains which form and the ways in which the domain walls move is not repeatable. Thus, the formation of a multi-domain state in the free layer 38 leads to domain wall movement, thereby producing non-linearity and noise in the sensor signal. Such non-linearity and noise are undesirable in the MR head 50 during operation.
There is an additional limiting factor to the height of the conventional MR sensor 30. As magnetic flux travels up the conventional MR sensor 30, away from the recording media 40, flux leaks out of the conventional MR sensor 30. The shield 14 and 22 and the shields 52 and 62 are significantly larger than the conventional MR sensor 30. Thus, magnetic flux leaks out of the conventional MR sensor 30 and into the shields 14, 22, 52 and 62. The height at which virtually all of the magnetic flux has leaked out of the conventional MR sensor 30 is defined as the flux decay length. If the conventional MR sensor 30 is made longer than the flux decay length, the additional height of the conventional MR sensor 30 will contribute to the resistance in the MR head 50, but not to the magnetoresistance. Any additional height of the conventional MR sensor 30 will, therefore, be a source of parasitic resistance and thus be wasted.
Accordingly, what is needed is a system and method for providing a MR head which is capable of reading information stored on magnetic recording media at higher densities and in which is less subject to noise due to domain wall motion. The present invention addresses is such a need.
The present invention provides a method and system for providing a magnetoresistive head that reads data from a recording media. The method and system comprise providing a first shield, a second shield, a magnetoresistive sensor, at least one insulating bias layer and a lead. The first shield has a first end, a central portion and a second end. The first end is closer to the recording media during use than the second end. The second shield has a first end, a central portion, and a second end. The first end of the second shield is closer to the recording media during use than the second end of the second shield. The first end of the second shield is preferably separated from the first end of the first shield by a read gap. The central portion of the second shield is preferably separated from the central portion of the first shield by a distance that is greater than the read gap. The magnetoresistive sensor is disposed between the first shield and the second shield and has a front end and a back end. The front end of the magnetoresistive is closer to the recording media during use than the back end. The front end of the magnetoresistive sensor is electrically coupled with the first end of the first shield or the first end of the second shield. The at least one insulating bias layer is magnetically coupled to the magnetoresistive sensor and magnetically biases at least a portion of the magnetoresistive sensor. The lead is electrically coupled with the back end of the magnetoresistive sensor. Thus, current is driven through the magnetoresistive sensor in a direction substantially perpendicular to the recording media during use.
According to the system and method disclosed herein, the present invention provides a magnetoresistive head in which current is driven substantially perpendicular to the recording media. The magnetoresistive head has reduced signal instability due to domain wall formation and domain wall motion in the magnetoresistive sensor. In addition, the magnetoresistive head preferably has an increased flux decay length. The increased flux decay length can be taken advantage of because the direction in which current is driven. Consequently, the MR head may also be capable of reading higher density recording media.